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Astron. Astrophys. 353, 25-40 (2000)

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7. Conclusion

We summarize the main conclusions of our analysis of the [FORMULA] AGNs from the ROSAT surveys in a wide range of depths:

  1. Like previous works, we find a strong evolution of the SXLF up to [FORMULA] and a levelling-off beyond this redshift.

  2. We have tried to find a simple analytical description of the overall SXLF. Our combined sample rejects the classical PLE model with high significance. The PDE model has been marginally rejected statistically and also overproduces the soft CXRB.

  3. We have found that an LDDE form (LDDE1), where the evolution rate is lower at low luminosities, gives an excellent fit to the overall SXLF. The extrapolation of the LDDE1 form produces [FORMULA] of the estimated extragalactic soft CXRB.

  4. Another form of LDDE (LDDE2), which equally well describes the overall SXLF from our sample, produces [FORMULA] of the extragalactic soft CXRB. These two LDDE models may be considered as two possible extreme cases when one considers the origin of the soft CXRB.

  5. The evolution of the number density of luminous QSOs in our sample has been compared with that of optically- and radio-selected QSOs. Our data are consistent with constant number density at [FORMULA], while optically- and radio-selected QSOs show a rapid decline. The statistical significance of this difference is just above 2[FORMULA]. Including more deep ROSAT surveys would trace the behavior with a better significance.

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© European Southern Observatory (ESO) 2000

Online publication: December 8, 1999